Abstract: A thermal processing method is described in which a temperature response of a substrate may be controlled during a heat-up phase or a cool-down phase, or during both phases. This reduces the thermal budget of the substrate and improves the quality and performance of devices formed on the substrate. In particular, by controlling the rate of heat transfer between the substrate and a thermal reservoir (e.g., a watercooled reflector plate assembly), the temperature response of the substrate may be controlled during the thermal process. The rate of heat transfer may changed by changing the thermal conductivity between the substrate and the thermal reservoir, by changing the emissivity of a surface of the thermal reservoir, or by changing the distance between the substrate and the thermal reservoir. The thermal conductivity may be changed by changing the characteristics of a thermal transport medium (e.g., a purge gas) located between the substrate and the thermal reservoir.